Organ with reed resonators



Jame m, 1%? W. M UNCH, JR 3,327,046

ORGAN WITH REED RESONATORS Filed Aug. 19, 1963 2 Sheets-Sheet 1 INVENTORWALTER MUNCH, IR.

ATTORNEY5 June 2@, W. UNC R ORGAN WITH REED RESONATORS 2 Sheets-Sheet 2Filed Aug. 19, 1963 INVENTOR R MUNCH, JR

ATTORNEY5 United States Patent 3,327,046 ORGAN WITH REED RESONATORSWalter Munch, Jr., Covington, Ky., assignor to D. H. Baldwin Company,Cincinnati, Ohio, a corporation of Ohio Filed Aug. 19, 1963, Ser. No.303,084 21 Claims. (Cl. 84-123) This invention relates generally toelectro-mechanical resonators and more particularly to organ tonegenerating systems employing such resonators.

In the art of organ tone generation by electronic circuitry, the needfrequency arises for a high Q resonator, Qs of the order of 50 beingespecially desirable because resonators may be employed to controlwaveform envelopes and a Q of about 20400 provide favorable rise anddecay times for various musical tones in the audio band. It follows thattype of resonators which may find application in electronic musicalinstruments preferably should be capable of adjustment of Q, but alsosuch resonators should be relatively temperature insensitive in respectto tuning, and the frequency values should be constant with drivingvoltage, i.e. with amplitude of vi- 'bration of the resonator.

In the past it has been common to utilize high Q electrical resonantcircuits as resonators for tone generating systems. In order to attainthe values of Q which are required, resort has been had to toroidalcores in the inductances of the circuits, which are expensive. In afairly complex organ system a very large number of resonators may berequired, and economic considerations then become predominant. Accordingto the present invention, use is made in organ tone forming systems ofelectromechanical resonators, which may be fabricated economically andwhich have the desired electrical and mechanical characteristics. Theinvention concerns itself with the resonators per se (which may haveother uses than those described in the present invention) and furtherconcerns novel systems, which utilize such resonators, for generatingorgan tones.

The present invention is related in subject matter to an application forUS. patent filed in the name of Wayne, Ser. No. 46,704 filed Aug. 1,1960, entitled Electric Organ, and assigned to the assignee of thepresent application, and which concerns an organ system in whichharmonic rich generators apply their output to a series of semitonefilters, which individually select the semitones into separate channels.The signal content of the separate channels is then processed andcombined to produce a tone having a desired frequency spectrum. Thefilters employed to separate the semitones may have desirablecharacteristics apart from the stated function, i.e. they may havesufliciently high Q to impart a relatively long build up time or onset,and a relatively long decay, to the individual tone components.Furthermore, they may be slightly detuned with respect to their drivingsignals, in order to establish transient responses which are musicallydesirable, and they may introduce chiif. Chili components may beintroduced into an organ tone in response to transient excitation ofcertain of the resonators, which may not be driven in steady state forthe particular tone, more specifically, a chitf resonator may betransiently excited in response to and during onset of excitation ofanother resonator which is to be excited in steady state. In the Wayneapplication purely electrical high Q resonators are employed, but thesuggestion is made that electro-mechanical resonators may be employedinstead.

The resonators of the present invention are further useful in an organtone generating system disclosed in a copending application for U.S.patent, in the name of Cunningham, Ser. No. 302,968 filed August 19,1963, entitled, Chiff and Tone Generator, and assigned to the assignee3,327,046 Patented June 20, 1967 of the present application. In thesystem of Cunningham a square wave or sine wave generator system isemployed, and for each tone an electrical resonant filter or resonatoris employed, tuned to the fundamental of the tone, and having a Qselected to insert an appropriate rise and decay time into the waveenvelope of the response of the resonant filter to the generator output.The filters may also be detuned with respect to the generatorfundamental frequency in order to impart a variation of frequency duringtone onset and decay, due to the combination of steady state response ofthe resonator with its transient response, these occurring at thedriving frequency and at the filter resonant frequency, respectively.The response of the filter is applied to a harmonic generator, theoutput of which constitutes a frequency spectrum appropriate for tonegeneration and the tone may be further formed, as required, by means oftone forming filters, the latter operating in a manner generally wellunderstood in the art of org-an tone production.

In both the Wayne application and the Cunningham application chili? isintroduced into certain of the organ tones. For example, chili? iscommonly found in the flute tones of pipe organs. The serious musiciandesires an electronic organ to simulate the tones of pipe organs andaccordingly desires particularly to insert chiff into flute tone outputsof the electronic organ. Some difference of opinion appears to existamong musicians in respect to precise definitions of chitf. In the caseof flute tones, it is agreed that chiff consists of a transient,gradually rising and gradually decaying frequency component equal toabout 5.5 times the fundamental frequency of the flute tone, and whichoccurs only during the build up of the flute tone. In the case of theharmonic flute the chili may be at a sub-harmonic frequency. Somewriters on the subject believe that chili is always accompanied by windnoises, but this is disputed. It is also disputed whether transientfrequency components which occur during onset only, and which maycorrespond with a harmonic or subharmonic, or any partial, of thefundamental frequency of a given tone, as distinguished from anun-harmonic or sub-harmonic frequency, may properly be denominatedchiif. For the purpose of the present application any of these transientfrequencies having a suitable transient wave shape, and which serve tosimulate the onset quality of any tones of a pipe organ more closelythan would be the case otherwise, are denominated chiff. In the Wayneapplication chiif is produced by shock exciting a resonator especiallyselected for the purpose. In the Cunningham application, on the otherhand, chiff is produced by applying, to an oscillator, a gating Wavewhich keys on the oscillator at the onset of a tone, and which modulatesthe amplitude of the oscillator during the onset of the tone in such away as to generate or simulate chiff. The electromechanical resonatorsof the present invention have been found valuable for the purpose ofproducing chiif effects, in organs of both the Wayne and the Cunninghamtypes, more particularly, though not exclusively, because suchresonators have been found to possess a transient response atapproximately flute tone chiif frequency, i.e. about 6.3 times thefundamental frequency applied to the resonator.

It is, accordingly, a primary object of the present invention to providean improved electr-o-mechanical resonator.

It is a further object of the invention to provide a novel reed typeelectro-mechanical resonator which is driven by a piezo-electric driver,and which is found to have the property that an onset transient occurson energization by a driving voltage without a corresponding decaytransient when the resonator is tie-energized in respect to its drivingvoltage, which may be a step function voltage.

It is still another object of the invention to provide anelectro-mechanical resonator of the tuning fork type in which the tinesof the fork are composite, each tine being composed in part of apiezo-electric element and in part of an element fabricated of othermaterial, having a different density or different Youngs modulus, orboth, and which more particularly has the characteristic that its Youngsmodulus does not appreciably vary with the amplitude of its vibration.

Still another object of the invention resides in the provision of anelectro-mechanical resonator in which the tines are piezo-electricelements.

A further object of the invention resides in the provision of a tuningfork employing tines having'piezo-electrio drivers, or consisting ofpiezoelectric elements, in which the location of the electrodes on thetines is selected to reduce the amplitudes of certain modes of vibrationof the tuning fork. 1

Electro-mechanical resonators employing piezo-electric drivers or inwhich the piezoelectric element constitutes the resonating component ofthe resonator are found to have responses or modes of vibration, whichmay be undesirable. In the case of tone generating systems, such modesintroduce undesired tonal components, which must be eliminated byfiltering. In the case of a flexural mode of vibration of a mechanicalresonator, a mode of vibration occurs at 6.3 times the fundamental modeof the resonator, and many additional modes may occur, these severalmodes being of relatively high amplitudes, sometimes approaching that ofthe fundamental. Accordingly, in resonators intended to be employed intone generating systems, it is essential that the undesired modes bereduced in amplitude as far as possible, although for some purposes oneor more of the modes may be musically useful.

A problem occurs, especially in musical instruments, of mountingelectro-mechanical resonators so that they will not be subject toexternal shock and vibration. This is accomplished according to thepresent invention by designing the resonators in a tuning forkconformation, so that there will exist one point of the fork which isalways a node for all modes of vibration simultaneously and using thatpoint for mounting the resonator. It is thereby economically feasible toreduce intercoupling between forks.

It is desirable that electro-mechanical resonators be electro-staticallydriven because such resonators may be expected to be fabricated atreduced cost. The use of coils for driving resonators inevitably becmoesexpensive. However, piezo-electric crystals employed as resonators arenot feasible because impedances involved are extremely high and becauseit is difificult to fabricate such crystals in required shapes for audioapplications, i.e. as elongated rods. For example, a length ofapproximately 2 may be required for about a 100 c.p.s. resonator, andthe length and thickness may be measured in a :few hundredths of aninch. Resonators of very many different lengths and different operatingfrequencies are required for application to a single organ, and the useof crystals for so many different frequencies would be prohibitivelyexpensive.

In accordance with the present invention use is made of ceramicpiezoelectric resonators because of their reasonable cost, ease ofdesign for audio frequency operation, and their excellent mechanicalproperties. Use further is made of composite resonators, i.e., if aresonator is in the form of tuning fork each time of the tuning fork iscomposed of a piezo-electric section and a nonpiezo-electric section. Itis then found that by properly selecting the length of the piezoelectricsection with respect to the total length of the tine, certain modes ofvibration may be de-emphasized.

Ceramic piezo-electric material varies in Youngs modulus over aconsiderable range of value in accordance with stress. This means thatwhen the material is used as a resonator the resonant frequency of theresonator becomes a function of the driving voltage. Moreover, when theresonator is utilized because of its slow response property, in formingthe envelopes of tones, frequency may vary as the tone builds up, with acorresponding build up of mechanical vibration amplitudes. This effectmay involve a variation of frequency of more than 1%, which is audiblyobtrusive. By utilizing spring steel, for example, for a large portionof the length of the tine and piezo-electric material for the remainderof the tine, or by building the tines entirely of spring steel havingcemented thereto piezo-electric driving elements, the tonal frequencyshift with amplitude of vibration may be radically reduced, since springsteel has a Youngs modulus which does not appreciably vary withdeflection. While spring steel has been suggested as a suitable timematerial, this is not requisite. Other materials may be selected whichhave the required resilience to form resonators having desired Q values,and spring steel has been found to represent merely one example of asuitable material.

A further broad object of the invention resides in modes of inclusion ofelectro-mechanical resonators in electronic organ tone generators, totake advantage of the properties of such resonators which are notavailable in purely electrical resonators.

The above and still further objects, features and advantages of thepresent invention will become apparent upon consideration of thefollowing detailed description of one specific embodiment thereof,especially when taken in conjunction with the accompanying drawings,wherein:

FIGURE 1 is a block diagram of an organ tone generator, according to theinvention;

FIGURE 2 is a view in elevation of a tuning fork resonator according tothe invention, useful in the system of FIGURE 1; 1

FIGURE 3 is a view in plan of a modification of the resonator of FIGURE2;

FIGURES 4a, 4b and 5 are wave forms useful in explaining the'inventionof FIGURES 1-3;

FIGURE 6 is a sketch of a functional equivalent of a tuning forkresonator;

FIGURE 7 is a view in plan of a modification of the resonator of FIGURES2 and 3;

FIGURES 8, 9, 10 and 11 are block diagrams of modifications of thesystem of FIGURE 1.

Referring now more particularly to FIGURE 1 of the accompanyingdrawings, the reference numeral 10 denotes an oscillator, which may be asine wave oscillator for the purposes of the present invention but whichpreferably is a square wave oscillator since such oscillators may befabricated more cheaply than sinusoidal oscillators in the audiofrequency range. In series with the oscillator 10 may be provided asource of DC voltage 11. As will appear as the description proceeds, thesource of DC voltage 11 is not necessary, but is advisable, when asquare wave generator is employed, but is necessary when a sinusoidalgenerator is employed. A mechanically resonant filter 12 is connected tothe generator 10 via a key switch 13, operated by a key of an electronicorgan. Mechanically resonant filter 12, the details of which will bedescribed hereinafter by reference to other figures of the accompanyingdrawings, has a fundamental response frequency equal to the fundamentalfrequency of the generator 10. Further the mechanically resonant filter12 has a transient response frequency in a second mode, equal to about6.3 times the fundamental frequency of the generator 10. The Q of theresonator 12 is assumed to be approximately 50. Assuming that thegenerator 10 has a fundamental frequency of about c.p.s., an appropriaterise time will be available in the resonator 12 to provide simulation ofthe rise times of certain organ tones. For other organ tones a differentrise time may be desirable and accordingly the Q of the resonator 12 maybe adjusted to suit the application, in a manner to be describedhereinbelow. I

Resonator 12 has a second mode transient response at 6.3 times thefundamental response, as has been above explained. This frequencyapproaches with reasonable closeness to a chiif frequency suitable forthe fundamental frequency, although perfect chiif frequency should,according to some writers on the subject, be 5.5 times the fundamentalfrequency. According to the modification of the present invention asillustrated in FIGURE 1, the output of the resonator 12 is applied inparallel to two low Q band-pass filters. One of the filters, 14, whichmay be a band-pass filter having sufficient width that it does notmodify appreciably the response of the resonator 12, selects thefundamental response of the filter for further application in the tonegenerating system. The other filter, 15, selects the chiff component ofthe filter response. The output of the filter 14 alone is applied to aharmonic generator 16, various examples of which are disclosed in theabove mentioned Cunningham application. The spectrum generated by theharmonic generator 16 may be applied to a tone forming filter 17. Thegenerator 16 and the filter 17 together form a tone simulating one oranother of the tone types appropriate to electronic organs. The outputof the tone filter 17 is applied to suitable amplification system 18,and is radiated acoustically by a loudspeaker or other analogous device19. The output of the chiif filter is applied to the input of theamplifier 18, so that the chiff plus the fundamental tone may becombined. Chitf is a tone component which is required to occur only atthe onset of a tone and not at its decay and furthermore is a componentwhich requires a relatively slow buildup and slow decay during the onsettime of the main tone and does not occur during the steady state of themain tone. Accordingly, the resonator 12, in order to produce a chiifcomponent of a generated tone is required to have peculiarcharacteristics, not normally found in resonators. Appropriatecharacteristics are inherent in resonators fabricated according to thepresent invention, and illustrated in FIGURES 2, 3 and 4 of the presentinvention.

Referring now to FIGURE 2 of the drawings, there is illustrated a tuningfork configuration 20 having tWo tines 21 and 22 joined by a bridgingelement 23 at one end of the tines, the remaining ends of the tinesbeing free to vibrate in the flexural mode. While such a tuning fork mayhave many modes of vibration, at the center point 24 of the bridgingelement 23 all these modes of vibration have Zero amplitude. Accordinglycenter point 24 is utilized as a mounting point for the tuning fork 20.Point 24 is suspended from a helical spring 25 which may extendvertically, in a mounted and operating tuning fork, and spring 25 mayextend from the central point of a horizontally extending helical spring26, the ends of which are secured to mounting posts 27, 28. Each tine iscomposed of a spring steel rod 29 which constitutes an extension of thepiezo-electric rod 30, and is cemented thereto at point 31 for thatpurpose.

Signal may be applied at terminal 33, and abstracted at terminal 39. Thebridging element 23, when fabricated of metal, may be utilized as aground or common point for the system.

Use of a composite tine has great advantage in the system. It is foundexperimentally that tines of purely piezo-electric ceramic have aconsiderable variation of frequency with driving amplitude or drivingvoltage applied to terminal 33. This occurs because Youngs modulus forthe material involved varies with strain. This is an extremelyundesirable property from the point of view of a music instrument. Inorder to reduce the impact of this property steel is used as a majorportion of the tines. In one specific embodiment of the invention, forexample, Where the tines have a total length of 2" and are designed forresonance at 100 c.p.s., the piezo-electric element may have a length of1.6. The remainder of the length is made up of spring steel. However,the length of the piezoelectric element may be reduced to 6 for exampleso that the major part of the tine is spring steel. The total length ofpiezo-electric element employed is a function of the voltage sensitivitydesired for the system, and the total length of piezo-electric elementcannot be reduced indefinitely without seriously reducing the output ofthe system for a given signal input. A compromise value must be reached,for which variation of resonance frequency is acceptable. Wherevariation of resonant frequency of the order of l /2% is acceptable theentire tine may be fabricated of pieZo-electric material, as in FIGURE3, Where the tines 4t) and 41 are no longer composite tines but aretotally piezo-electric. In the system of FIGURE 3 the electrodes 42, 43for the time and 44, 45 for the tine 41 do not extend over the entirepiezo-electric body. Accordingly, while the entire tine is made ofpiezo-electric material, and has a length resonant to the frequencyinvolved, the entire tine is not electrically active. The theory onwhich is based the effectiveness of reduced electrical length for apiezo-electric vibrator is that for all modes above the first thecrystal has both positive and negative curvature. The phase of theoutput voltage generated by the crystal is dependent upon the sign ofthe curvature. Thus there is a point along the crystal at which thevoltage caused by the positive curvature of the crystal cancels thevoltage caused by the negative curvature of the crystal. While it isimpossible, according to the available experimental evidence, toeliminate all modes by selection of length of electrode in relation totine length, any given mode can be reduced by a factor of over 30 db,and for some electrode lengths a great many of the higher modes may beradically reduced simultaneously. For example for a tine 1.9" long, forwhich the electrode length extends 1.1 from the mount end, it is foundthat the third mode can be reduced over db, the 4th mode over db, the5th mode over 50 db, while the first mode is attenuated only about 7 or8 db and the second mode only about 20 db.

For the application of the resonators of FIGURES 2 and 3 to tonegenerating systems for electronic organs, the second mode is oftendesirable but the remaining modes are undesirable. Accordingly, the factthat the second mode cannot be radically reduced is not of seriousimport. However, if it were desired to highly attenuate the second modealso this might be possible by appropriately selecting the electrodelength for one of the tines so as to minimize the second mode and forthe other tine so as to minimize the remaining modes.

In addition, it is possible to load the crystal, for example as inFIGURE 3, wherein are shown loads 50 in the form of masses positioned soas to vary frequency. Each of the modes has a point at which vibrationis a maximum. For the first mode vibration amplitude is a maximum at thefree end of the tine. For the other modes it occurs at other points. Byapplying mass loads to the points of the tine at which a given modevibrates at maximum amplitude, the frequency of that mode can be varieddifferentially with respect to the other modes because the other modesdo not vibrate at maximum amplitude at that same point. In FIGURE 2 isshown the utilization of mass loads 51 at the ends of the tine. Thisvaries the frequency of the resonator in the fundamental or first mode.

The total mass of the bridging element 23 is important because as thismass is varied the coupling between the tines is varied. Eventually apoint is reached at which the coupling between the tines is sufiicientlygreat that the two tines constitute critically coup-led circuit. Suchcircuits, in their transient response, are quite different than singlycoupled circuits, under coupled circuits or overcoupled circuits.

In FIGURE 4a of the accompanying drawings is illustrated the transientresponse of an essentially singly resonant tube circuit to which hasbeen applied a step voltage of the type illustrated in FIGURE 5. It willbe seen that the oscillations rapidly attain a very high or maximumamplitude, when the step function commences, and decays as a function oftime according to the Q of the resonator.

Such a response is not suitable for the tonal characteristic known aschiff. The latter requires a gradually built up transient followed by agradually decaying transient rather than a transient which builds upvery suddenly and then decays. However, the transient response of acritically doubly tuned circuit, which is illustrated in FIGURE 4b doesapproximate the envelope characteristic of chiff, and accordingly theresonators of FIGURES 2 and 3 may be designed to provide appropriatetransient characteristic for utilization in chiff generators by suitablycoupling the tines. This may be best accomplished by suitably reducingor increasing the mass of the bridging element 23, on an empiricalbasis. One of the important characteristics of the resonators of FIGURES2 and 3 is the transient response of these filters in the second mode.This is a mode which is particularly, though not exclusively, useful forproduction of chilf. The production of chiff requires a transient atonset on the main tone, but must not occur at decay of the main tone.The reason why a resonator of the type of FIGURE 2 has the requisiteonset transient for the fundamental tone, but not for its decay relatesto the character of the resonator. For the fundamental frequency, atransient occurs when the driving signal is removed, as well as when itis applied, assuming that the fundamental frequency of the resonator isequal to or substantially equal to the driving frequency. If the drivingfrequency is not equal to the resonant frequency of the resonator, thenas the driving frequency is switched on, the resonator is shock excitedby the driving frequency, but is also driven by the driving frequency.The two frequencies initially exist together, causing a peculiar beatingeffect which is musically very pleasant. This effect, however, existsonly during onset of the wave because the transient component dies outin a time determined by the Q of the resonator, leaving only the steadystate. Moreover, the steady state becomes a constant amplitude in duecourse, and then represents the fundamental of the tone being generated.The sole effect on the steady state of the detuning of the resonator isthat the response is at lower amplitude than would be the case were theresonator precisely tuned. In the case of the second mode, however, thisis not true since there is no driving frequency corresponding with thesecond mode vibration. Accordingly, the second mode vibration is solelya transient response. FIGURE 6 of the accompanying drawings represents amechanical equivalent of a tuning fork. To the terminal 60 may beapplied a step function, i.e. may be applied a DC. steady state voltageon closure of the switch 61. The driving tine of the resonator isexemplified by a resonator 62 having electrodes 63, 64. Mechanicalcoupling between the tines is exemplified by the line 65 and the driventine is represented by the crystal 66, the output terminal being 67.When the switch 61 is closed a voltage appears across the electrodes 63,64, which is applied to the elements 62. The resonator 62 is then shockexcited and vibrates in its various modes, transiently. One may assumethat the coupling between the resonators 62 and 66 is so slight that thecircuit looks like a singly coupled circuit to the driving stepfunction. In such case there would be a rapid or instantaneousinitiation of the transient at maximum amplitude, which will decay as afunction of time to zero as in FIGURE 4a. When the switch is opened, onthe other hand, the voltage on the electrodes 63, 64 remains because theelectrodes constitute a capacitor. That voltage will decay very slowlythrough any leakage path which may exist, the latter being representedby resistance 68, or an actual resistance may be inserted at theposition 68. Accordingly, there is no rapid decay of applied voltage atthe resonator 62 when switch 61 is opening, and there is no ringingforce applied on decay of the tone. The distinction then is that whenthe switch 61 is closed, a sudden voltage is applied to the electrodes63, 64 but when the switch 61 is open the contrary effect, i.e. a suddenreduction of voltage does not occur. If now the coupling 65 issufficiently great the resonators 62 and 66 look like a criticallycoupled circuit. In such case, when the switch 61 is closed the initialtransient starts at 0 and builds up to some predetermined value andthereafter decays to 0, as indicated in FIGURE 4b of the drawings. Thisoccurs in the system of FIGURE 1, for the second mode because for thesecond mode only a transient voltage is applied, i.e. either a stepfunction, in the case of a voltage supplied by the battery 11 of FIGURE1, or in absence of the battery by the level of the square wave 10 whenswitch 13 is closed. Battery 11 is particularly useful in the case ofsine wave excitation, because for sine wave excitation the point in thecycle of the sine wave at which the switch closes is indeterminate. Theswitch may be closed when the sine wave is small or when it is verylarge and in each case the transient response would be different, sincethe transient response is a function of the ringing impact, i.e. thevalue of the voltage at the moment the switch is closed.

The piezo-electric elements of FIGURES 2 and 3 are flexural elements,which implies that each element is composed of two differently polarizedceramic layers in a sandwich. For some purposes it is desirable toutilize a ceramic piezo-electric device which operates in thelongitudinal mode. For such a mode only a single layer of ceramic isrequired. This single layer, as at 70 in FIG- URE 7 may be cemented to atine 71 of a steel tuning fork '72 and may have a single electrodeplated thereon as 73, the tine itself constituting another electrode, ifdesired, or two electrodes may be provided on the ceramic, as iscommonly the case when the ceramics are purchased commercially. InFIGURE 7 the ceramic is operated in the longitudinal mode, i.e. it has alength determined by the voltage applied thereto. This is not true ofthe tine since the latter is made of steel. The combination of the twoeffects, i.e. elongation of ceramic 70 without a correspondingelongation of the tine 71 causes a bending of the tine 71 andaccordingly causes tuning fork action.

Various ways of employing the resonators of FIGURES 2, 3 and 7 in organsystems, in addition to that indicated in FIGURE 1 of the accompanyingdrawings are envisaged. In FIGURE 8 the output of the resonator 12,including its second overtone at approximately 6.3 times thefundamental, are applied in toto to the harmonic generator 16. Thesystem being otherwise the same as in FIGURE 1. The harmonic generator16 then generates harmonics of the chiff frequency as well as harmonicsof the steady state frequency and the chiff now is a relatively complexchiff instead of being essentially a single frequency chiff. Theadvantage of the system of FIGURE 8 over the system of FIGURE 1 is thattwo filters are eliminated from the system of FIGURE 1 and thedisadvantage is that the chiff component is not a pure tone, which itpreferably should be. Chiff is normally employed with pure flute tones,although various forms of chiff may also occur with other tones. For thepure flute tone very few harmonic tones are required, and accordinglyany harmonics provided by the harmonic generators may be of very lowamplitude, or may be non-existent. Accordingly, for flute tones inparticular, the requirement for separate fundamental and chiff filtersbecomes non-existent and the system of FIGURE 8 becomes entirelypractical.

In the system of FIGURE 9 two mechanical resonators are employed, i.e.connected in parallel with the switch 13 are resonator 12a and resonator12b. Resonator 12a is designed to have a minimum second mode as well asminimum 3rd, 4th, 5th mode, etc. Resonator 12b, on the other hand, istuned to about 5.5 times the fundamental frequency and also is designedto minimize all modes other than the fundamental mode. The resonator 12bis then shock excited, when switch 13 is closed, since the drivingfrequency provided by the oscillator 10 contains no component at 5.5times the fundamental. The resonator 12a is driven in the fundamentalmode. Accordingly, the resonator 12b provides a transient at 5.5 timesthe fundamental frequency on onset of the tone, i.e. when the keyswitch13 is closed, but, because of the considerations explained by referenceto FIGURE 6 of the drawings, there is no terminating transient.

In the system of FIGURE 10 two resonators are employed, identified bythe reference numerals 12c and 12a. These are designed to have the samefundamental fre quency. However the resonator 120 is designed tominimize the second mode, while the resonator 12d is designed to providea substantial second mode oscillation. The resonator 12d is not excitedby the generator 10 in the system of FIGURE 10 but is excited by a DC.source 60 which is connected to the resonator 12d by means of a keyswitch 61 ganged to the key switch 13. The resonator 12d is anovercoupled tuning fork which is designed to produce an envelope oftransient response appropriate to chiif production. The transientresponse of the resonator 12d then is composite, i.e. there is atransient response at the fundamental and there is a transient responsein the second mode, but there is no steady state response. The resonator12c produces only a fundamental response, or produces other thanfundamental mode responses which are greatly reduced in amplitude, andproduces its own transient onset and decay for the fundamentals. Theresonator 12d provides no transient on decay but only at onset, i.e. anytransient on decay is so slow as to be audibly ineffective. Theadvantage of the system of FIGURE 10 is that the two resonators may besimilar in many of their constructional features, which simplifiesfabrication, A further advantage is that two dilferent fundamentaltransient responses occur, at onset, which enhances the transientresponse of the finally generated tone. This system also enables easyselection of a desired chilf frequency.

FIGURE 11 is similar to FIGURE 10 except in that the resonator 1212 isoperated in its second mode, i.e. is resonant in its fundamental mode to5.5 times the frequency of the generator 10. The output of resonator 12eis a transient, since it is excited only by a chitf function.

Various other applications of the resonators of FIG- URES 2, 3 and 7 maybe envisaged, particularly by reference to the Wayne and the Cunninghamapplications, wherein are disclosed various forms of tone generatingsystems employing resonators.

While I have described and illustrated one specific embodiment of myinvention, it will be clear that variations of the details ofconstruction which are specifically illustrated and described may beresorted to without departing from the true spirit and scope of theinvention as defined in the appended claims.

What I claim is:

1. A transient generating system for an electronic organ having afundamental tone frequency, comprising a source of voltages, said sourceof voltages including a source of oscillations at said tone frequency, akey switch, an electromechanical resonator system, all in series, saidelectromechanical resonator system having a transient response mode atabout six times said fundamental tone frequency on switch closure andhaving essentially no transient response mode at subsequent switchopening.

2. An electronic organ tone generator, comprising in sequence, a sourceof voltages having a fundamental tone frequency, a key switching system,an electro-mechanical resonator system, said electro-mechanicalresonator system having a fundamental vibration mode at leastapproximately at said fundamental frequency and a second mode ofvibration, an output system in cascade with said resonator system, saidsecond mode having a frequency appropriate to generation of chiff forsaid fundamental tone frequency.

3. The combination according to claim 2 wherein said electro-mechanicalresonator system is a reed type resonator having a piezo-electric drive.

4-. The combination according to claim 3 wherein said reed typegenerator is a tuning fork.

5. The combination according to claim 2 wherein said resonator system isa pair of resonators, one of said resonators having a vibrating mode atsaid fundamental frequency, the other of said resonators having avibrating mode at about six times said fundamental frequency of said oneof said resonators.

6. The combination according to claim 5 wherein said resonators areconnected in parallel with respect to said output system.

7. The combination according to claim 5 wherein said last mentionedvibrating mode is a second mode of said other of said resonators.

8. The combination according to claim 5 wherein said last mentionedvibrating mode is a fundamental mode of said other of said resonators.

9. A system according to claim 2 wherein said source of voltagesincludes a DC. source and a source at the said fundamental tonefrequency, and wherein said key switching system includes separateswitches connected in series with said separate source.

10. In a tone generator for an electronic organ, a source ofoscillations, said oscillations including a component at frequency f, akey switch in cascade with said source, an electromechanical resonatorconnected in cascade with said key switch, a tone forming system incascade with said resonator, an output system in cascade with said toneforming system, a chiff generator, said chilT generator comprising asecond electro-mechanical resonator, an electrostatic drive for saidsecond electromechanical resonator, an output circuit for said secondelectro-mechanical resonator, means coupling said output circuit forsaid second electro-mechnical resonator to said output system, and meansresponsive to actuation of said key switch for applying only a shockexciting signal to said second electro-mechanical resonator, said shockexciting signal having no steady state component at any resonant mode ofsaid second resonator, said second resonator having a resonant mode atabout 5.5 times said frequency f.

11. A tone generator for an electronic organ, comprising a source ofvoltages including a component at a fundemental tone frequency, an organkey switching system operatively associated with said source, anelectromechanical resonator system connected to said switching systemfor application of said voltages to said resonator system on actuationof said switching system, said electromechanical resonator system havingat least a first vibrational mode adjacent to said fundamental tonefrequency and slightly displaced therefrom and a second vibrational modeat a frequency appropriate to generation of chili? components for saidfundamental tone frequency, the Q of said resonator at said fundamentaltone frequency being in the range 20 to and the frequency differencebetween said fundamental tone frequency and the frequency of said firstmode enabling substantial steady state response in said first mode atsaid fundamental tone frequency, said resonator system including atleast one resonator of tuning fork configuration and including at leastone electrostatic drive, a harmonic generator responsive to saidresonator system and an output system responsive to said harmonicgenerator and said resonator.

12. The combination according to claim 11 wherein said source ofvoltages includes a DC component.

13. The combination according to claim 11 wherein said resonator systemconsists of a single resonator.

14. The combination according to claim 11 wherein said resonator systemincludes a pair of resonators having resonant modes at least near saidchiff frequency and at least near said fundamental tone frequency.

15. The combination according to claim 11 wherein said source ofvoltages includes a source of alternating voltage and a source of directvoltage, and wherein said switching system includes separate switchesfor said alternating and direct voltages, and wherein said resonatorsystem includes separate resonators for said chiff and said tone.

16. In an electrical musical instrument,

a sine wave generator for producing an electrical steady state tonesignal corresponding with one frequency component of a musical note;

non-linear circuit means for adding steady state harmonics to saidsignal, thereby producing a steady state complex wave corresponding withsaid musical note,

key operated means for at will connecting said sine wave generator tosaid non-linear circuit means,

means connected between said key operated means and said non-linearcircuit means for altering the fre quency of said electrical signal, and

electro-acoustic means for radiating said complex wave, wherein saidmeans for altering the frequency of said signal is an electromechanicaldevice having a mechanical resonance frequency musically related to thefrequency of said steady state tone signal.

17. The combination according to claim 16 wherein said means foraltering the frequency of said signal is a means for only transientlyaltering the frequency of said signal.

18. The combination according to claim 17 wherein said means foraltering the frequency of said signal is an electromagnetic devicehaving a mechanical resonance frequency musically related to thefrequency of said steady state tone signal.

19. The combination according to claim 17 wherein is further providedmeans for adding a chiif component to said complex wave.

20. The combination according to claim 19 wherein said means for addinga chill? component includes a mechanically resonant device.

21. In a system for generating chifi,

an electromechanical voltage responsive resonator hav ing two voltageresponsive electrodes to which shock voltage may be applied to excitesaid resonator into shock excitation,

said electrodes being arranged and adapted to capacitively storeelectrical energy in response to said voltage,

resistance connected across said electrodes and having a value such thatsaid electrodes discharge said electrical energy at a sufliciently slowrate that said resonator is not shock excited during said discharge, and

switch means for applying said shock voltage across said electrodes atwill.

References Cited UNITED STATES PATENTS 2,989,886 6/1961 Markowitz 841.19

ARTHUR GAUSS, Primary Examiner.

J. BUSCH, Assistant Examiner.

1. A TRANSIENT GENERATING SYSTEM FOR AN ELECTRONIC ORGAN HAVING AFUNDAMENTAL TONE FREQUENCY, COMPRISING A SOURCE OF VOLTAGES, SAID SOURCEOF VOLTAGES INCLUDING A SOURCE OF OSCILLATIONS AT SAID TONE FREQUENCY, AKEY SWITCH, AN ELECTROMECHANICAL RESONATOR SYSTEM, ALL IN SERIES, SAIDELECTRO-MECHANICAL RESONATOR SYSTEM HAVING A TRANSIENT RESPONSE MODE ATABOUT SIX TIMES SAID FUNDAMENTAL TONE FREQUENCY ON SWITCH CLOSURE ANDHAVING ESSENTIALLY NO TRANSIENT RESPONSE MODE AT SUBSEQUENT SWITCHOPENING.